Mercury switch relay



Dec. 16, 1941.

c. H. LARSON 2,266,469 MERCURY SWITCH RELAY Filed Sept. 3, 1941 fig 39 IILIIIIIIIII Illlllllllllllll [/7l 6/7 for. Car/ H. Larson ffys.

, Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE 266,469 MERCURY SWITCH RELAY Carl H. Larson, Elkhart, Ind., assignor to The Adlake Company, a corporation of Illinois Application September a, 1941, Serial No. 4.09.400

(c1. zoo-112) 11 Claims.

The substance of the present invention was previously disclosed in copending application Serial No. 335,659, filed May 17, 1940, the disclosure of which is hereby made a part hereof by reference.

This invention pertains to mercury switches of the type in which the contacts are closed by a magnetically responsive armature, such as a mercury displacer, located within a stationary switch envelope. In the past, glass has been used in this type of switch for the envelope, and while it is entirely suitable for most uses of the switch, there are some occasions when it is desirable to have the switch envelope made of less frangible material. There are also times when particular conditions make'it desirable to use a high pressure gas fill. According to the present invention the problem is solved, after analyzing the various problems involved, by use of an envelope of metal, despite the assumption heretofore that metal envelopes could not be used in this type of switch.

An important object of my invention is, therefore, to provide a shock resistant displacer type mercury switch formed of materials which may be readily shaped within close dimensional tolerances.

Other objects are to provide improved means of joining together and sealing the metal walls of the switch, particularly sealing the tubular envelope to an end wall.

Other objects and'advantages-will become apparent from the description and drawing, in which:

Fig. 1 is avertical sectional view of my improved mercury switch; and

Fig. 2 illustrates another form of my invention, incorporating a modified switch envelope.

Referring to Fig. 1, the switch envelope H is tubular. in form, and has a uniform external diameter. The interior ispolished to decrease friction, and counterbored at each end, as shown at I3, toform an internal shoulder H. The envelope of this invention is formed of metal but nevertheless has both the characteristics of being substantially non-magnetic and of not amalgamating or otherwise harmfully combining with mercury under the conditions of use. It is capabio of being machined or formed within reasonably close dimensional tolerances. Because of their high strength, ready availability, and other desirable properties, I prefer to use ferrous alloys in forming my switch envelope, and I have found that steel property alloyed with sumcient amounts of manganese or chromium and nickel, or combinations thereof, have suitable non-magnetic properties. The non-magnetic properties of these alloys is believed to be due to the action of the alloying ingredients, which act to hold the iron in the form of austenite during the cooling process-sustenite being the non-magnetic form of iron. An example of such an alloy is stainless steel having an approximate composition of 18% chromium and 8% nickel (generally termed 18-8 steel"). I have found that this particular steel is well suited for use as an envelope material, particularly as it is both non-magnetic and resistant to wetting by mercury.

Another example is the steel known as Hatfield" steel, one of the best known examples of which has about l2.5-l3% manganese, 1.05-l.2% carbon, and .4-.8% silicon. Any other manganese steel having therein suflicient manganese (at least 9 or 10%) to maintain the steel in its austenitic form as it cools to the lower atmospheric temperatures can be used. However, no metal readily amalgamating with mercury should be used in suilicient proportions in any steel that is in contact with mercury to amalgamate appreciably under the conditions of use. Except for cost, tungsten or molybdenum could be used for'the switch envelope inasmuch as each is both non-magnetic and non-amalgamating. Any other non-magnetic metal, such, for

example, as brass, could be used, if plated on its inner side with chromium, or other metal which will not amalgamate under conditions encountered. The non-amalgamating metal used in this plating may even be magnetic, as iron, provided the plating is of such thinnessthat the tubular envelope as a whole is substantially nonmagnetic.

A specific steel of the general type known as 18-8 is Carpenter stainl'ess'steel No. 4:,- having a composition (beside iron) of chromium 18%, nickel 9%, and carbon .08.'l%. For commercial reasons this is probably the most desirable at the present time. The following description will, therefore, be confined to the use of this material, although it is to be understood that other alloys having similar non-magnetic and non-amalgamating properties may be substituted if desired.

It is important that the metal chosen for the switch envelope be essentially non-magnetic. A magnetically responsive displacer 33 moves within the switch to change the mercury level, and if the nvelope is of magnetic material the displacer may be held to the envelope by the magnetic force employed to actuate the switch, or the residual magnetism resulting therefrom. As the functioning of the switch depends upon the movement of the displacer, it is apparent that any force preventing such movement will also prevent the functioningof the switch, and as no air gap exists between the displacer and the envelope even a slight magnetic force in the envelop may have undesirable effects. Further- -more, the magnetic actuating force would be shunted away from the displacer by a magnetic envelope.

A cap, generally designated 85, consists of a metallic disk it, adapted to be received in the counterbore l3 and to fit snugly against the internal shoulders it. An opening'is provided in the disk it, to which is welded, or otherwise attached, a small metal tube ii. The thickness of the disk i8 is somewhat less than the depth of the counterbore 53, so that when the disk I6 is inserted within the counterbore against the shoulders id portions it of the envelope M will extend beyond the outer surface of the disk.

When it is desired to seal the cap Hi to the switch envelope ii the cap is inserted, as described, against the internal shoulders id, and the projecting portions it of the envelope are turned inwardly against the exterior portion of the disk it, thereby pressing the disk firmly' against the shoulders it. The joint between the.

turned-down portion it of the envelope ii and the outer surface of the disk it is subsequently sleeve. The upper end of the sleeve 24 has a shoulder. 28 formed integrally therewith, and fused to this shoulder is a ceramic tube 29, formed of a material, such as Alundum, which has substantially the same coeflicient of thermal expansion as the glass. erally circular in section. The upper end of the ceramic tube 29 forms an opening 32. The exposed portion 21 of the electrode 23 extends into the tube 29 and terminates below the lowest point of the opening 32.

I preferto form the entire electrode structure separately from the balance of the switch, and

to seal this sub-assembly into the switch envesealed withhard solder, as indicated at W, or by 7 other suitable material, to form a strong gastight joint. Thedisk may also be welded ,in-

place, if desired, and it may be of any suitablemetal not amalgamating with mercury, as stainless steel, ordinary iron, or a metal known in the trade as Kovar," manufactured by Stupakofi Laboratories, Pittsburgh, Pennsylvania.

A base 29 consists of a disk of metaladapted to be received in the counterbore 03, in a manner similar to that described in connection with the cap 95, and is provided with an opening 22 in which an electrode 23 may be positioned. The disk ii is formed of a metal having a coefiicient of thermal expansion substantially equal to that of hard glass and molybdenum. A metal hav-- ing these characteristics is commercially available under the trade name of Kovar, and consists essentially of an alloy of iron, cobalt and nickel. The electrode i3 is preferably of molybdenum, and is covered for a portion of its lope in a manner similar to that described in connection with the cap 15.

The displacer, generally designated 33, is telescoped overthe electrode assembly, and may consist of a tube 35 of magnetic material, such as iron, telescoped over a sleeve 36 of insulating material, such as glass, the latter sleeve being somewhat longer than the tube 3%. The ends of the iron tube 34 are reduced in external diameter, forming an external shoulder 31. Guide. washers it are fitted over the insulating sleeve 36 and the reduced portion of the iron tube 36 against the external shoulders 31, and may be of the type described in my Patent No. 2,060,811.

These washers serve to prevent any appreciable sideward movement of the displacer assembly 33 by contact with the inner walls of the switch envelope ll. I

Coil springs 38 are fitted over the projecting ends of the interior insulating sleeve 35, and irictionally engage said sleeve to maintain the component parts of the displacer assembly 38 in their proper relation. These springs are of non-magnetic material, and serve to prevent the sticking of the displacer to either the cap 15 or the base 2i, and are particularly necessary when the cap is formed of a magnetic material, such as iron.

As the switch envelope it serves as one of the electrodes of the switch, it is often desirable, but not essential, to provide means of insulating the envelope II from other adjacent external por- 7 tions of the switch assembly, and from accidental length by insulating sleeve 2&1 of hard glass, such as Corning G-705 AJ, which has a coefiicient of thermal expansion substantially'equal to that of molybdenum and Kovar. sleeve. 2% is preferably heat bonded to "the electrode 23. The electrode 23 and the insulating sleeve-2Q are positioned within the opening 22 in the base 26 by forming bulges or shoulders 26 in the insulating sleeve, adjacent to both sides of the opening 22, and subsequently applying sufiicient heat to cause the glass to bond to the base 2i. This forms a strong gas-tight seal, as the electrode, the glass and the base all have ap- The insulating.

contact or short circuiting. This may be conveniently accomplished by mounting the assembled switch mechanism within a rigid tube 39, having a length somewhat greater than that of the switch mechanism. The tube 39 may be suitably formed of an insulating material, such as Bakelite, and the switch assembly held within the tube by applying a suitable sealing mate rial, such as sealing wax, to the ends of the tube after the switch mechanism is positioned therein, as indicated at ii.

If the switchassembly is to. be mounted within an insulating tube, it is necessary to provide means of forming a connection with the elec-= trodes, vizz-the switch envelope ii and the centrally positioned electrode 23. This may be accomplished by attaching a connecting wire 62 to. the switchenvelope at any desired point, the wire being of suficient length to extend beyond the tube 39. Electrode 23 may also be joined with a proximately the same coemcient of thermal expension. I The insulating sleeve 26 surrounding the electrode 23 extends into the switch envelope "II for slightly less than half the distance between the base 2i and the cap l5, and serves -to insulate the electrode from con t with the base 25 and the mercury fill, except for a portion 21 of the electrode which extends beyondthe insulating connecting wire in a similar manner, or extended beyond the tube. Connecting wires of this nature may be attached to the switch when the tube 39 is not employed.

A coil 53, having an iron circuit it, is provided with an opening in which switch assembly is positioned. Pole sleeve db may be provided fitting around the tube 3e and in contact with the iron circuit G5 to define an air gap M.

This shoulder 28 is gen- 2,2ce,4eo 3 If the coil is to be energized by an alternating current, the pole sleeves 46, or the iron circuit 44, or both, may be split to overcome the undesirable magnetic effects of such current, as high eddy current loss. This split need not extend completely across the iron circuit, but may be positioned on the portions lying above and below the coil 43, extending from one edge 01' the iron circuit 44 to the opening in which the switch envelope is positioned. The split in the pole sleeves should be axial, and sufiicient in width to prevent contact of the edges of the sleeve when positioned around the switch. The magnetic portion 34 of the displacer 33 may also be split in a similar manner.

The pole sleeves 46 are not essential, but are desirable, as they render the switch more sensitive to small exciting currents in the coil, and the action of the displacer 33in response to the coil may be controlled within certain limits by adjusting the position of the air gap 41.

The switch may be conveniently maintained in position within the coil 43 by means of a rubber sleeve 48, frictionally engaging the insulating tube 39, or the switch envelope ll if the insulating tube is not employed. The sleeve 48 is cylindrical in form and has a central opening of a diameter slightly less than the external diameter of the tube 39 or the switch envelope. The upper portion of the sleeve 48 is reduced in diameter to receive a bracket 49, of rigid material, which is adjustably secured to the iron circuit 44 by means of a machine screw 5!. The external diameter of the lower portion of the rubber sleeve 48 is greater than the diameter of.

the opening in the coil 43, so that the switch'is prevented from moving downwardly by the frictional engagement of the sleeve 43 with the tube 39. Upward movement of the switch assembly is prevented by the bracket 49, which may also be used to deform the rubber sleeve 48 into firmer contact with the tube 39 or with the switch envelope II, as the case may be. Other types of switch envelope th tube I1 is closed in a suitablemanner, as by pinching and welding; indicated sure, either above or below that of the atmosphere, but I prefer to use relatively high pressures, on the order of 100 pounds to the square inch, as I have found that inert gas, particularly quickly quenching any are formed when the circuit through the electrodes is made or broken, and gives a higher break-down potential. In certain instances even higher pressures may be between the base 2| and the cap l5. This is below theelevel which may be called the contact level of the electrode 21; i. e., the level to which the mercury must rise to complete the circuit. The opening 32 of the ceramic cup 29 determines the contact level in the illustrated form, and is above the low level of the mercury when the around the exposed portion 21 of the electrode 23, and in operation will always retain a certain amount of mercury in constant contact with and covering the exposed portion of the electrode. The air gap 41 is positioned somewhat below the displacer 33. When the coil is energized the displacer 33 is drawn downwardly, causing the mercury to rise within the envelope II and contact the pool of mercury remaining within the sleeve 29 through the opening 32, thereby completing the circuit between the electrode 23 and the switch envelope ll. When the coil 43 is deenergized the displacer 33 will rise, due to its own buoyancy, causing the mercury level to fall within the envelope and break the contact between the electrode and the switch envelope.

' Due to the large area of the foot electrode or.

switch envelope II, the contact resistance of my switch is extremely low, thereby making it eflicient to operate. The switch is also highly resistant to damage by accidental blows, and may therefore be used under circumstances which would prohibit the use of a switch having a glass envelope.

In place of the rigid tube 39 sleeves 18, of insulating material, may be interposed between the pole pieces 46 and the switch envelope H, as seen in Fig. 2, to insulate the iron circuit 44. The switch may be supported in the same manner as that previously described, with the rubber sleeve 48 in direct contact with the switch envelope H.

Fig. 2 illustrates particularly a modified form counterbore l3 at the open end of this envelope,

as well as the internal and external diameters 1 hydrogen at these pressures, has the property of employed, as the efliciency of the inert gas in quenching the arc increases with its pressure.

The displacer 33 floats on mercury fill'52 when the coil is deenergized, the amount of mercury in the envelope l I being such that when the displacer 33 is in its deenergized position the level of the mercury will be approximately half way and the capacity, "are the same as those previously described. An opening 9| is provided in the closed end of the envelope, to which the small tube l1, similar to that described in Fig. 1, may be attached by welding or otherwise. This tube may also be sealed in a similar manner. The remaining parts of the switch are similar to those described in Fig. 1. The switch operates in a manner similar to that previously described.

This particular type of switch envelope pos-v sesses certain advantages, particularly in that one of the seals, viz: that formed between the cap and the envelope, is eliminated by this type of envelope. This feature is important in my switch, for, as previously mentioned, I prefer to use high gas pressures, and the envelope must, therefore, be sufficiently strong to safely retain the gas, and the omission of one seal avoids that source of possible defect in the seal.

The resistance to wetting, by mercury, of the metals referred tofor envelope II and the disks l5 and 2| seems to be advantageous in connection with the seals. With such metals the mercury is unable to penetrate between the envelope H and the disk 2| to reach th solder IS with which it might amalgamate. At present, non-amalgamating metals are also non-wetting. Of course, if a non-amalgamating metal, which is wet by creasing both the safety and mercury under the conditions encountered, were found, and the illustrated seal were found unnon-wetting characteristics of the metal will have kept the mercury out of the clearances at low pressure, and the entrapment of the gas will dependably keep the mercury away from the solder on the outside of the seal, even at high I pressure. As a matter of fact, there will rarely be any clearances, especially if the projecting portion of the envelope H is upset and pressed against the disk 26 with considerable pressure, as in. a press.

Due to its simple and efficient construction, my switch'is capable of operating on extremely low exciting currents, and as it has very low contact resistance it is efficient in operation. The

materials from which the switch is manufactured are not subject to break-down under excessive loads, and are strong and durable, thereby indurability of the switch. The preferred metals .for envelope ll have an electrical resistance about forty times that of copper, and there is no danger that, with an alternating exciting current, eddy currents will be set up in the envelope of suflicient value to require an objectionably higher exciting current. Likewise, when direct current is used there will be no objectionable lag in the deenergization upon opening the energizing circuit. The high strength and impervious nature of the metal switch envelopepermits the advantageous use of a high pressure gas fill which cannot, of course, be safely used in conjunction with the conventional type of glass switch envelope. One

tion with mercury under normal switch operating conditions, a quantity of mercury, an electrode within said envelope and insulated therefrom, a

magnetically responsive displacer associated with said electrode, and magnetic means for changing the condition of the electrical circuit through' said mercury without movement of the switch envelope.

3. For use in a mercury switch of the class described, a switch envelope having side walls of non-magnetic material comprising iron in its non-magnetic form, and being further characterized by being substantially non-amalgamatim with mercury whenunder the influence of an electrical current.

4. A mercury switch assembly including an envelope, a quantity of mercury within the envelope, an electrode at times completing a circuit through the mercury, and magnetically responsive means within the envelope adapted to be actuated by means external 01 the envelope for changing the condition of the electrical circuit through the mercury, characterized by the pro- 1 vision of a substantially non-magnetic metal wall as part of the envelope, at least the inner surface of said wall being formed of a metal which resists amalgamation with the mercury under velope, a quantity normal switch operating conditions.

5. A mercury switch assembly including an enof mercury within the envelope, an electrode at times-completing a circuit through the mercury, and magnetically r'esponsive means within the envelope adapted to reason for the preference for the 18-8 type of steels is that the walls, when polished, may be relatively thinand still be impervious.

The joint formed between the switch envelope and the cap or base will retain the high gas pressures within the switch indefinitely, and is particularly eificient in this respect when compared to similar joints in other types of switches employing rubber ,or other organic materials as a sealing medium.

The foregoing descriptionhas been by way of illustration only, and it is to be understood that the specific embodiments herein described are merelyexamples of the many ways in which my invention may be embodied within the scope of the appended claims. The claims, therefore, are to be construed as broadly as the prior art will permit.

Iclaim asmy invention? l. A mercuryswitch assembly comprising, in

combination, a switch envelope having side walls' of electrically conductive non-magnetic material resistant to amalgamation-with mercury under normal switch operating conditions, a quantity of mercury and an electrode within said envelope,

and magnetically responsive means for changing the condition of the electrical circuit through said mercurywithout movement of'the switch envelope. 1.. g

2. A mercury switch assembly comprising, in

combination, a switch envelope having side walls of non-magnetic metal resistant to amalgamanormal switch operating conditions 6. A mercury switch assembly including an en- V velope, a quantity of mercury within the envelope. an electrode at times completing a circuit through the mercury, and magnetically responsive means within the envelope adapted to be. actuated by means external of the envelope for changing the condition of the electrical circuit through the mercury, characterized by the provision of ,a

substantially non-magnetic metal wall as at least part of the envelope, at least the'inner surface of said wall being formed of a metal-whichresists amalgamation with the mercury and wetting by mercury under normal switch operating conditions.

'1. A mercury switch assembly including an envelope, a quantity of mercury within the enthrough the mercury,

velope, an electrode at times completing a. circuit through the mercury, and magnetically-responsive means within the envelope adapted to be actuated by means external'of the envelope for changing the condition of the electrical circuit haracterized by the provision of a substantially non-magnetic metal wall as part of the envelope; the inner surface of said wall being coated with a substance-that is substantially non-amalgamating with the mercury under normal switch operating conditions.

8; A mercury switch assembly including an envelope of electrically conductive material, a

quantity of mercury within the envelope, an electrode sealed through the envelope and insulated therefrom, said electrode at times completing a circuit through the mercury, and magnetically responsive means within the envelope adapted to be actuated by means external of the envelope for changing the condition of the electrical circuit through the mercury, characterized by the,

provision of a substantially non-magnetic metal wall as part of the envelope, the inner surface of said wall being coated with a substance that is substantially non-amalgamating with the mercury under normal switch operating conditions.

9. A mercury switch assembly comprising in combination a switch envelope having side walls formed of stainless steel that is both non-magnet and resistant to amalgamation with mercury under normal switch operating conditions, a quantity of mercury, an electrode within said envelope and insulated therefrom,'a magnetically responsive displacer associated with said electrode, magnetic means for changing the condition of the electrical circuit through said mercury without movement of the switch envelope,

'means for hermetically sealing the ends of the envelope, a high pressure gas fill for the envelope, the inner surface of said stainless steel side wallsbeing polished to make said walls substantially impervious to the high pressure gas fill.

10. A mercury switch assembly including an envelope, a quantity of mercury within the envelope, an electrode at times completing a circuit through the mercury, and magnetically responsive means within the envelope adapted to be actuated by means external of the envelope for changing the condition of the electrical circuit through the mercury, characterized by the provision, as part of the envelope, of a substan tially non-magnetic wall, composed of iron in its austenitic form, at least the inner surface of said wall being formed of a metal which resists amalgamation with the mercury under normal switch operating conditions.

11. A mercury switch assembly including an envelope, a quantity of mercury within the envelope, an electrode at times completing a circuit through the mercury, and magnetically responsive means within the envelope adapted to be actuated by means external of the envelope for changing the condition of the electrical circuit through the mercury, characterized by the provision of a substantially non-magnetic metal wall as part of the envelope, at least the inner surface of said wall being formed of a metal which resists amalgamation with the mercury, and further characterized by the provision of a gas fill above the mercury within the envelope comprising a gas having no reaction with materials with which it comes in contact under the conditions of use at a. pressure at least approximately as high as pounds per square inch.

CARL H. LARSON. 

